Natural mineral bentonite as catalyst for efficient isomerization of biomass-derived glucose to fructose in water

Abstract The development of inexpensive and efficient heterogeneous catalyst for the conversion of biomass including food and winery processing waste to value-added products is crucial in biorefinery. Glucose could be obtained via the hydrolysis of waste cellulose or starch-rich material, and the isomerization of glucose to fructose using either Lewis acid or Bronsted base catalysts is an important route in biorefinery. As a natural clay mineral, bentonite (Bt) is widely used as adsorption material and catalyst support, but how its intrinsic acid-base properties can impact the biomass conversion chemistry is still rarely reported. In this study, we investigated the influence of the textural and acid-base properties of Bt on the glucose isomerization reaction. The reaction kinetics and mechanism, and the effect of Al3+-exchange were explored. The results showed that the activation energy of Bt-catalyzed glucose conversion was 59.0 kJ mol-1, and the in-situ Fourier transform infrared spectrometer (FT-IR) characterization proved that Bronsted base was responsible for the isomerization. The highest fructose yield of 39.2% with 86.3% selectivity could be obtained at 110 °C for 60 min in water. Alkaline rinse and calcination can recover most of the catalytic activity of the spent catalyst.